1. Field of the Invention
The present invention relates to a pantograph-type jack and, more particularly, to a screw bar for a pantograph-type jack.
2. Description of the Prior Art
A conventional pantograph-type jack such as that shown in Japanese Utility Model Publication No. 57-15911 is known. A conventional pantograph-type jack, such as that shown in FIGS. 1A and 1B, includes a pair of lower arms 2, a pair of upper arms 3, a load-receiving plate 4 pivotally connecting the upper arms, and a base plate 5 pivotally connecting the lower arms and supporting the jack. The left-side upper and lower arms are pivotally connected to a nut member 6, and the right-side arms are pivotally connected to a bearing member 7. A screw bar 10 pivotally supported by the bearing member is threadably engaged with the nut member, and the load-receiving plate is raised and lowered by the rotation of the screw bar 10, in a manner well known in the art.
A joint portion 11 is fixed to one end of the screw bar 10, and a crank handle (not shown) or the like is engaged with the joint section 11. Accordingly, the screw bar 10 is rotated by the operation of the crank handle.
In the conventional jack shown in FIGS. 1A and 1B, the joint portion 11 is fixed to the screw bar 10 by a connection screw 12, which is shown in FIG. 1B, that necessarily has a smaller diameter than the screw bar 10. The joint portion 11 is fixed to the screw bar 10 with the connection screw 12 through a washer 13. The washer 13 is interposed between the screw bar 10 and the joint portion 11 to provide a bearing surface contacting bearing 7 and to prevent the joint portion 11 from loosening.
Construction of the conventional pantograph-type jack thus requires a specially formed joint portion 11 in addition to the screw bar 10, and the number of parts is increased. Furthermore, dimensional accuracy must be increased to prevent looseness at the connection between the connection screw 12, the screw bar 10, and the joint portion 11. Moreover, the connection screw 12 must have a small diameter, in comparison with the other portion of the screw bar 10, so that the mechanical strength of the connection of the joint portion 11 to the screw bar 10 is decreased.
An object of the present invention is to provide an improved screw bar for a pantograph-type jack that obviates the aforementioned disadvantages of the illustrated conventional screw bar.
A further object of the present invention is to provide an improved screw bar having high reliability.
A still further object of the present invention is to provide an improved screw bar that includes a minimum number of parts.
Additional objects and advantages of the present invention will be set forth in part in the description that follows and in part will be obvious from that description or can be learned from practice of the invention. The advantages of the invention can be realized and obtained by the apparatus particularly pointed out in the appended claims.